Methods of producing metallic compositions comprising amalgams



United States Patent ce 3,154,413 METHODS 6F PRODUCENG METALLIC COMPU-SETIUNS COMPRISING AMALGAMS Robert Henry Dow, Stretford, England,assignor to Associated Electrical Industries Limited, London, England, aBritish company No Drawing. Filed July 5, 1961, Ser. No. 121,817

Claims priority, application Great Britain July 8, 1960 7 Claims. (ill.75-l35) The invention relates to methods of producing metalliccompositions comprising am-algams and especially to such compositionssuitable for use in the precision casting of intricate objects.

More particularly an object of this invention is to provide a means ofproducing metallic compositions which can be moulded to complex metalshapes with a minimum expenditure on tooling and process plant. The mostcommon way of producing such shapes is by casting, in which field therehas been considerable development in the art of precision casting. Thedevelopment of new materials such as plastics, and processes such aspowder metallurgy, has provided a greater degree of flexibility inmanufacture. However, these processes sulier from a number ofdisadvantages from the manufacturing or technical points of view; forexample, components produced by powder metallurgy require hard metalmoulds and result in a product which is weak in tension. There has beena need for a process which is as simple to operate as cast resins, butwhich results in a product more comparable to a metal casting. Thisinvention is directed towards this end.

Amalgams have been used for a considerable number of years by the dentalprofession and in more recent years proposals have been made for theproduction of copper amalgam by mechanically compounding copperparticles with mercury, the copper being taken into solution in themercury. To produce such a compound in bulk by these methods is adifi'icult operation, and it is an object of the invention to provide amethod of producing, in bulk, metallic compounds including amalgamsbetween various metals and mercury suitable for precision casting.

According to the present invention in the production of a metalliccomposition of a powdered metal with mercury, the powdered metal, beforemixing with the mercury, is plated with an intermediary metal whichreadily amalgamates with mercury and which is present only in smallproportions so as to have little or no elfect on the properties of thefinal compound. Such intermediary metal is a metal other than copper.The plating of the intermediary metal is applied without external meansfor producing electric potentials such as are known in electroplatingand may be done in aqueous solution.

The plating is preferably applied by treatment with a solutionconsisting of, or containing, a salt of the further metal, such solutionhaving the property of removing, without eroding the metal, impuritiessuch as oxides, and oil from the surf-ace of the particles of thepowdered metal and to deposit upon the said particles a very thin butcontinuous film of the said further metal, such further metal havin gthe property of resisting rap-id oxidation and amalgamating readily withmercury.

Powdered copper is suitable for such method and it has also been foundthat other metals such as cobalt, iron, nickel and zinc can also bereadily compounded with meronly if subject to such a pretreatment. Theintermediary metal may be, for pxarnple, palladium or tin.

The treatment solution may in general comprise an acid solution of asuitable salt of the further met-a1 referred to above which metal may bea precious metal or a non-precious metal.

In one example of the method according to the inven- 3,l5l,ll3 PatentedOct. 27, 1964 tion wherein finely powdered copper is compounded withmercury, the treatment solution consists of an acid solution ofpalladium chloride, for example a one percent solution of palladiumchloride in normal hydrochloric acid.

The invention is applicable also to the compounding of other powderedmetals with mercury, for example, iron, nickel and zinc. Furthermore thesalts of metals other than palladium may be used in the treatmentsolution. For example where the deposited metal is tin the platingsolution may contain stannous chloride.

in the examples given above the metal powders may be washed in palladiumchloride, but it should be appreciated that other plating solutions arepossible, and in fact, are necessary with certain metals; for examplepalladium chloride is not a suitable pretreatment solution for aluminumpowder.

The particle sizes for which the method can be successfully employedinclude the range from 600s mesh down to 4-5 microns. These are notlimitations imposed by the nature of the method and it is obvious thatthe lower limit may extend below 4 microns.

It is desirable that the solution used shall remove all impuritiesincluding inter alia oxides and oils, from the surface of the particlesyet not erode the metal itself. It is also necessary that the solutionshall impart to each particle a very thin but continuous film of a metalwhich does not oxidize rapidly but amalgamates readily with mercury.Several such solutions are possible. For example 1% palladium chloridein normal HCl. In the case where the plating metal is tin, a tin platingsolution containing stannous chloride may be used.

The electrodeless plating operation used by the invention has thefollowing points in its favour:

(1) No elaborate equipment required.

(2) The amalgams, although wet, are produced rapidly.

(3) When treating the smaller particle sizes 45 microns, for example,the particles are made heavy in that they tend to cluster together andsink to the bottom of the container, enabling them to be washed withoutloss, and making it easier to bring them into contact with the mercury.These small particles are of particular importance :as their largesurface area to volume ratio cuts down the time and work required tobring the amalgam to a critical stage.

The term critical stage refers to the stage at which there is suificientof the powdered metal dissolved in the mercury for the amalgam to set asopposed to the state in which the metallic particles are merely coatedwith mercury. Critical solutions in mercury of copper, nickel, and zincand other metals are obtainable in this way. The product of the methodmay find application, for example, in the manufacture of spark-machiningelectrodes. One such material would be copper-tungsten, which is knownfor its resistance to arc-erosion and used as an arcing horn in airblast circuit breakers.

Example I For the bulk preparation of a mercury-copper composition usingthe palladium chloride solution, the copper powder is first weighed intoa vessel, then thoroughly wetted with a small quantity of water. Thepalladium solution is added and the powder agitated until a blackprecipitate of metallic palladium is seen. The powder is washed and therequired quantity of mercury added. Further agitation produces anamalgam which can be dried, moulded into pellets, and stored for futureuse.

Example II For making an iron amalgam grams of 600 mesh iron powder isWetted thoroughly with a small quantity of water 30 cc. of 1%palladium-chloride in normal hy drochloric acid is added and the mixtureis agitated and afterwards rinsed; than 60 grams of mercury is added.Further agitation produces the amalgam.

Example III For making a nickel amalgam 100 grams of nickel powder (ofsize 4-5 microns) is wetted thoroughly with a small quantity of water,to which is added 50 cc. of the palladium-plating solution followed byagitating and thorough rinsing. Mercury-say 60 grams-is then added andthe mixture agitated further to produce the amalgam.

If to be used immediately, the amalgam may then be moulded to thedesired shape using a suitable pattern and allowed to air harden. 'If itis desired to use amalgam which has been previously prepared and storedin pellet form, the pellets are warmed gently until small beads ofmercury appear on the surface. The amalgam may be then moulded as abovedescribed. After the amalgam has set it is removed from the mould andheated in a sealed furnace in a reducing or inert atmosphere for thepurpose of removing and recovering the mercury.

What I claim is:

1. A method of producing a metallic amalgam suitable for use in theprecision casting of intricate objects comprising the steps of treatinga powdered metal selected from the group of copper, iron, nickel, zinc,and mixtures thereof with an electrodeless hydrochloric acid platingsolution of palladium chloride to deposit a thin film of readilyamalgamated palladium metal on said powdered metal, and agitating thecoated metal powder in contact with mercury to form an amalgam.

2. A method as claimed in claim 1 wherein said plating solutioncomprises a 1% solution of palladium chloride in normal hydrochloricacid.

3. A method of compounding finely divided metal powders with mercury toproduce mouldable pellets comprising the steps of treating a powderedmetal selected from the group of copper, iron, nickel, zinc and mixturesthereof with an electrodeless hydrochloric acid plating solution ofpalladium chloride to deposit a thin film of read ily amalgamatedpalladium metal on said powdered metal, agitating the coated metalpowder in contact with mercury to form an amalgam, drying theamalgamated powder, and moulding the dried amalgamated powder intopellets.

4. A method according to claim 3 wherein said plating solution comprisesa 1% solution of palladium chloride in normal hydrochloric acid.

5. A method according to claim 4 wherein said powdered metal is copper.

6. A method according to claim 4 wherein said powdered metal is iron.

7. A method according to claim 4 wherein said powdered metal is nickel.

References Cited in the file of this patent UNITED STATES PATENTS HarrisJan. 3, 1893 Clancy July 4, 1961 OTHER REFERENCES

3. A METHOD OF COMPOUNDING FINELY DIVIDED METAL POWDERS WITH MERCURY TOPRODUCE MOULDABLE PELLETS COMPRISING THE STEPS OF TREATING A POWDEREDMETAL SELECTED FROM THE GROUP OF COPPER, IRON, NICKEL, ZINC AND MIXTURESTHEREOF WITH AN ELECTRODELESS HYDROCHLORIC ACID PLATING SOLUTION OFPALLADIUM CHLORIDE TO DEPOSIT A THIN FILM OF READILY AMALGAMATEDPALLADIUM METAL ON SAID POWDERED METAL, AGITATING THE COATED METALPOWDER IN CONTACT WITH MERCURY TO FORM AN AMALGAM, DRYING THEAMALGAMATED POWDER, AND MOULDING THE DRIED AMALGAMATED POWDER INTOPELLETS.